Agriculture Reference
In-Depth Information
Chapter 3
ABA Transmembrane Transport
and Transporters
Mitsunori Seo
Abstract Two different types of abscisic acid (ABA) transmembrane transporters,
the ATP-binding cassette (ABC) type and the NRT1/PTR FAMILY (NPF) mem-
ber proteins, have been identified in Arabidopsis ( Arabidopsis thaliana ). Previous
studies indicated that ABA is actively synthesized in cells that are located around
the vasculature in response to water deficit. This observation suggests that ABA
has to be translocated to the guard cells to induce stomatal closure. In accord-
ance with this hypothesis, the gene encoding an ABA exporter (AtABCG25)
is expressed in vascular tissues, whereas the gene encoding an ABA importer
(AtABCG40) is expressed in guard cells. The expression of another ABA importer
gene ( AtNPF4.6 / NRT1.2 / AIT1 ) in the vascular tissues implies that the balance
between ABA export from and ABA import back into the vascular tissues deter-
mines the amount of mobile ABA present in the apoplastic space. The existence of
closely related homologues in the AtABCG and AtNPF members that might func-
tion as ABA transporters suggests that ABA transport is regulated in a complex
manner.
Keywords ABA · Transmembrane transport · Transporters · Regulation
3.1 Passive and Active ABA Transport Across Biological
Membranes
Movement of abscisic acid (ABA) within plants has been shown in several ways, for
example, in experiments using radioisotope-labeled ABA as a tracer and by graft-
ing between ABA-deficient mutants and wild-type plants (Ikegami et al. 2009 ; Frey
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